They don't want anyone to have any fun. They want you to stay celibate (especially men, who they want to use to plunge the whole world into the Second Dark Ages so they can make their own laws). Facebook can get around that--and the hounders will have a miserable time trying to trash you before you get around to anything there.
And, they will do whatever they have to. Using fake usernames, impersonating apostates, and these friend requests all allow the hounders and hounder-hounders to get into the accounts. Once there, they will look through your bulletin boards, forum posts, and blog posts as well as private chats. If they find something they can use against you, they will print it out and bring it to the hounding call. From there, it's their option as to what to do next: disfellowship or kidnap (and enslave).
Making it difficult involves using an avatar that does not include your own picture (and, in fact, could mislead any hounders) and a handle that they cannot guess who they are looking at. Give your real name only by private message (if at all), or by regular e-mail (and then only if you have a legitimate reason to). They will still see the posts and bulletins, but will have a miserable time proving that it is you.
That is, unless you do not want to pio-sneer. You get the application shoved in your face, and mutter "I think I will go home tonight and open a MySpace or Facebook account". The slip will end up in the garbage--especially if they can find your profile. The best part is you can do both, and tell them only about one (and use a different handle and avatar on the other, where you really trash the witlesses).